1. Field of the Invention
The present invention relates to a recording thin-film magnetic head used for a floating magnetic head, or the like, and more particularly, it related to a thin-film magnetic head having an excellent heat-dissipation characteristic by optimizing the structure of a toroidal coil layer.
2. Description of the Related Art
A recording thin-film magnetic head (inductive head) having core layers and a coil layer has made a progress on the path to miniaturization due to a requirement for a high recording density in recent years; as a result, the coil layer must be formed by winding in a very fine space.
The known coil layer is generally formed by winding around a connecting portion connecting the lower and upper core layers, using a space formed between lower and upper core layers. The coil layer formed in such a way of winding is called a spiral coil.
However, the spiral coil has problems in that, for example, it is difficult to effectively provide a necessary winding number in a fine space; hence, it is believed that the structure of the inductive head formed by winding in a toroidal shape around the core layers serving as a winding shaft will be a main stream in future.
For example, Japanese Unexamined Patent Application Publication No. 5-250636 (hereinafter, referred to as Patent Document 1) has disclosed the structure of the coil layer formed by winding in a toroidal shape around the core layers constituting the inductive head. By using such a toroidal coil layer, a three-dimensional space around the core layers can be effectively utilized, whereby it has been expected that miniaturization of the inductive head can be achieved and magnetization efficiency will be improved.
However, the compact inductive head equipped with the toroidal coil layer especially has the following salient problem. That is, Joule heat generated due to a recording current passing through the coil layer and heat generated due to eddy currents generated in the cores are unlikely to be effectively released from the inductive head; as a result, a temperature in the inductive head becomes very high.
When the temperature in the inductive head becomes high, a portion where the inductive head is formed is more likely to protrude from the opposing surface opposed to a recording medium than the other portion due to a difference in thermal expansion coefficients between the coil layer and the core layers, both composed of a metal material, and an insulating material covering the peripheries thereof.
In particular, in the thin-film magnetic head in which a high recording density is achieved, since a recording current supplied to the toroidal coil has a high frequency, a temperature in the inductive head rises suddenly, thereby resulting in an increased amount of protrusion of the inductive head from the opposing surface opposed to the recording medium. Thus, when the inductive head protrudes from the opposing surface opposed to the recording medium as described above, the inductive head is likely to more often come into collision with the recording medium, whereby the recording medium and the inductive head are likely to be damaged.
The foregoing problem cannot be solved even with the structure of the inductive head set forth in Patent Document 1. Patent Document 1 describes connection between lower and upper stripe-shaped conductive films constituting the toroidal coil, having a structure in which an electrically bonding portion between the lower and upper stripe-shaped conductive films is made wider than other portions of the same, overlapping with a magnetic core.
When FIG. 1 and other figures shown in Patent Document 1 are viewed, the upper stripe-shaped conductive film has a very narrow portion overlapping with another magnetic core, both ends of the upper stripe-shaped conductive film are bent toward a direction (this direction is generally called a height direction) along which the foregoing both ends are distanced away from a base-plate end surface, and the bent portions are made gradually wider. The base ends of the foregoing both ends constitute “an upper lead wire” and “a terminal” mentioned in this disclosure.
Heat generated in the inductive head is easily transferred in the coil layer composed of a thermally conductive metal such as copper (Cu). However, with the structure set forth in Patent Document 1, the portion of the coil layer overlapping with the magnetic core is very narrow, thereby resulting in a very low efficiency of thermal conductance in this portion. Also, in Patent Document 1, although both ends of the coil layer are wider than the portion of the same overlapping with the magnetic core, thermal transfer paths extending to wide both ends are too narrow because of the very narrow portion overlapping with the magnetic core, whereby heat is unlikely to be released to both ends.
Hence, with the structure of the toroidal coil in Patent Document 1 as described above, heat generated in the inductive head is unlikely to be effectively released outside; as a result, it is believed that, since a temperature in the inductive head becomes high, it is difficult to effectively reduce an amount of protrusion of the toroidal coil from the opposing surface opposed to the recording medium.